1. Field of the Invention
The present invention generally relates to the field of a disk drive including a perpendicular magnetic recording system, particularly to a technique of write compensation which compensates for recording distortion resulting from magnetic disturbance.
2. Description of the Related Art
In recent years, a perpendicular magnetic recording system has attracted attention as a technique for exceeding the limit of recording density in the longitudinal magnetic recording system in the field of disk drive represented by a hard disk drive.
Additionally, in a conventional disk drive including the conventional longitudinal magnetic recording system, a nonlinear bit shift occurs in magnetic recording data recorded on a disk medium so that the magnetization transfer position (signal reverse position) shifts forward from the normal position by the influence of an adjacent bit pattern. Such a recording distortion phenomenon degrades the error rate during data reproduction (read operation).
To solve this, a write compensation operation for correcting magnetization transfer into the normal position is executed during the write operation. For the principle of the write compensation function, since the bit shift amount depends on the adjacent bit pattern, the bit shift amount (including direction) is predicted, the write timing is delayed, and as a result the magnetization transfer is corrected into the normal position.
On the other hand, in the disk drive including the perpendicular magnetic recording system, the magnetization transfer position shifts from the normal position in accordance with the adjacent bit pattern, but the direction differs from that of the longitudinal magnetic recording system. The recording distortion phenomenon occurs such that the transfer position shifts backwards. Therefore, in general, the write compensation function of allowing the write timing of the magnetization transfer to precede the normal position is required in the perpendicular magnetic recording system.
A write compensation method has heretofore been proposed which comprises: predicting a magnetization reverse position by the adjacent bit pattern beforehand in a recording signal series; and setting forward or delaying the magnetization reverse timing in accordance with the adjacent bit pattern (e.g., see Jpn. Pat. Appln. KOKAI Publication No. 2000-207704).
In recent years, a single pole type head has been used as a write head in a disk drive including the perpendicular magnetic recording system. Moreover, a double-layered disk medium is used as a disk medium.
The single pole type head includes a main pole and auxiliary pole, and magnetizes in a perpendicular direction (depth direction) of the disk medium with a recording magnetic field generated in the perpendicular direction from the main pole. Additionally, for example, a giant magnetoresistive (GMR) element is used in a read head similarly as the longitudinal magnetic recording system. The write head and read head are separately mounted on the same slider in the disk drive.
Moreover, a double-layered disk includes a recording layer indicating magnetic anisotropy of the perpendicular direction, and a soft magnetic layer between the recording layer and a substrate. The soft magnetic layer draws a magnetic flux generated from the main pole of the write head during the write operation so that the flux passes through the recording layer in the perpendicular direction, and guides the magnetic flux to the auxiliary pole. The soft magnetic layer has a function of supporting a so-called data recording operation.
In the disk drive including the above-described system, recording efficiency is high. However, when the disk is influenced by the magnetic field due to the magnetic flux floating outside (magnetic disturbance), recording distortion by nonlinear bit shift occurs particularly in the recording data on the disk right under the write head with a high possibility. Such a recording distortion phenomenon cannot be compensated by a read channel, and degrades the error rate during data reproduction. Therefore, a write compensation function is required against the magnetic disturbance, but the write compensation method according to the above-described related art cannot solve the problem because the bit shift by the magnetic disturbance is not assumed.